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In Reply to: RE: OK, Great ........................ posted by Tre' on March 27, 2021 at 08:40:01
nt
Follow Ups:
I wanted to stay away from your 270Hz crossover point but make sure to limit the low bass as much as possible to your output transformer.
If you're 270Hz crossover is 6db then you could use a .00056uf cap instead and get rid of the passive 270Hz crossover part but that would leave your horn subject to any bumps that might happen in the amp so it would not be as safe.
Or, if your 270Hz crossover is 12db then you could change it to 6db and have 6db at 270Hz before the amp and 6db at 270Hz after the amp and still be safe-ish.
But let's not get too off track. Limit the low bass to the amp and enjoy the improvement.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Seems a bit hard to find for me..
Edits: 03/27/21
http://www.soniccraft.com/index.php/film-capacitors-rel-cap-rte-c-301_48
I'm having trouble too.
Why is the grid resistor 1 meg?
You could get two 1000pf (.001uf) and two 500pf (.0005uf)
Place one 1000pf in parallel with one 500pf. That would be one .0015uf cap and that will work.
Against the 1meg grid resistor it would make a 6db per octave high pass filter with a -3db point of 106Hz.
https://tubedepot.com/products/silver-mica-1000pf-500v?utm_source=google&utm_medium=cpc&adpos=&scid=scplpCP-SM-1000-500V&sc_intid=CP-SM-1000-500V&gclid=EAIaIQobChMIvYjtuKbR7wIVfyGtBh1UYgR_EAQYBCABEgJiAvD_BwE
https://tubedepot.com/products/silver-mica-500pf-500v?utm_source=google&utm_medium=cpc&adpos=&scid=scplpCP-SM-500-500V&sc_intid=CP-SM-500-500V&gclid=EAIaIQobChMIvYjtuKbR7wIVfyGtBh1UYgR_EAQYASABEgJ2uPD_BwE
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
What do you think of these?
https://www.ebay.com/itm/0015-uF-1500pf-630-volt-Polystyrene-Capacitor-NOS-QTY-20-ea-P510/192162051515?hash=item2cbdc035bb:g:fJQAAOSwE1xbyhgr
or
https://www.ebay.com/itm/2-NOS-Vintage-Pyramid-0015-uf-300v-PIO-Capacitors-Vitamin-Q-Oil-Treble-Bleed/122629572318?hash=item1c8d4ac6de:g:TMAAAOSwjC9ZgoWT
or
https://www.ebay.com/itm/2-NOS-Vintage-Fast-0015-uf-300v-PIO-Capacitors-Vitamin-Q-Oil-Treble-Bleed-Caps/112507170078?hash=item1a31f32d1e:g:21wAAOSw3IdZgoZL
Polystyrenes are pretty good sounding caps.
I don't like PIO caps anymore, I use to.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I have a 3535Pf (.003535uf) Russian silver mica cap against a 330k ohm grid resistor for a -3db point of 136Hz. My midrange speakers are about 3db down and falling at 200Hz all by themselves. I use an electronic (opamp based) low pass filter at 200Hz. in front of the SS amp I use to drive my JBL 2231s woofers.I find the Russian silver mica caps to be very transparent. I use them in my phono preamp also.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 03/27/21 03/27/21
https://www.hificollective.co.uk/search/site?title=.0015
The Audio Note Tin Foil Capacitor is not to bad.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
"Why is the grid resistor 1 meg?"
I don't know, you'd have to ask Jeff Korneff :-)
It goes back to the Article in 'Glass Audio' to a Schematic from Eric Barbour, where Jeff Korneff got his initial design. Here is the Schematic from that Article.
It would be nice to use a Single Capacitor.
You can make that grid resistor just about any value you like.
I use the 330k on my first stage because it fits well and gives me the frequency I want with the sliver mica caps I had. And it's plenty high as to not load down my preamp.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Can't you get a capacitor close to crossover FQ and fine tune with the grid resistor value?
Wouldn't it be cheaper to swap out resistors than caps?
What formula do you use to calculate crossover FQ?
What can a 500 ohm output impedance preamp be comfortable with?
"Can't you get a capacitor close to crossover FQ and fine tune with the grid resistor value?"
That's what I do.
"What formula do you use to calculate crossover FQ?"
-3db point of the filter = 159155/(cap value in uf times resistance value)
"What can a 500 ohm output impedance preamp be comfortable with?"
Almost anything. The rule of thumb is 1:10 so it will drive 5k without trouble. Just don't forget about capacitance reactance at the high frequencies which is in parallel with the grid resistor value. That would include cable capacitance and the Miller capacitance of the tube being driven. Also the source needs to be able to supply the current that capacitance reactance will require.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
T
.
Have Fun and Enjoy the Music
"Still Working the Problem"
nt
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